Oriented coring is a technique used in drilling, and refers to the production of a core that is marked by a small groove. The position of this groove can be related to magnetic or true North. This allows core analysis to determine any bedding planes or fracture alignments to help geologists produce a three dimensional map of a structure. It also enables the analysis of directional porosity and permeability in fluvial deposits. This can help to define and examine the reservoir structure which can make any recovery of deposits more efficient due to use of suitable selected recovery systems.
It is known to perform oriented coring using a corebarrel modified at the bottom by a cutting mechanism which will cut three small grooves into the core. One of these grooves is identified as the main groove. The cutting mechanism is fixed in relation to the top part of the inner tube of the corebarrel by means of threaded connections in the inner tube. A magnetic multishot survey tool is run on top of the corebarrel surrounded by a non magnetic drill collar. This survey tool has its tool face aligned mechanically to the cutting mechanism which creates the main groove.
This system can give good but inconsistent results, mainly due to problems associated with the survey tool. These include:
1. No survey due to excessive downhole temperatures (fogged or melted film). PA1 2. Failure of the survey tool due to mechanical damage during coring. PA1 3. Failure of the survey tool due to "go-devilling" (battery pack). PA1 4. Good survey pictures but meaningless results (rotation of toolface or groove).
In addition, it is necessary to stop all rotation and pumps in order to get a good photographic picture, and this is not good drilling practice.
A similar previously-known system used solid state survey equipment which does away with the need for a camera and film. The tool using this system is capable of operating continuously whilst coring. The results obtained are generally similar to those using the photographic system, but the associated problems are reduced mainly due to the elimination of the film recording system.